The invention relates generally to improvements in the manufacture of expandable stents and, more particularly, to new and improved methods and apparatus for direct laser cutting of stents in providing stents of enhanced structural quality.
Stents are expandable endoprosthesis devices which are adapted to be implanted into a patient's body lumen, such as a blood vessel or coronary artery, to maintain the patency of the artery. These devices are typically used in the treatment of atherosclerotic stenosis in blood vessels, coronary arteries, and the like.
In the medical arts, stents are generally tubular-shaped devices which function to hold open a segment of a blood vessel or other anatomical lumen. Stents are very high precision, relatively fragile devices and, ideally, the most desirable stents incorporate a very fine precision structure cut from a very small diameter, thin-walled cylindrical tube. In this regard, it is extremely important to make precisely dimensioned, smooth, narrow cuts in the thin-walled tubing in extremely fine geometries without damaging the narrow struts that make up the stent structure. Prior art stents typically are cut by a laser and held by collet in a computer controlled machine that translates and rotates the stent as the laser cuts through the outer surface of the metal tubing. In order to stabilize the stent tubing, typically a bushing surrounds the stent tubing and is positioned between the laser and the collet holding the stent. Prior art bearings or bushings create a small amount of friction between the stent tubing and the bearing which can cause slight imperfections in the laser cutting process as the stent tubing is moved relative to the bearing.
Referring to FIGS. 1-3, a typical prior art laser assembly is shown in which a laser beam is used to cut a pattern in stent tubing. The stent tubing is mounted in the collet of a CNC controller which will move the stent tubing in a translational and rotational direction while the laser beam cuts through one wall of the stent tubing to form a pattern. As shown, a bushing is used to support the stent tubing between the collet and the laser beam (or proximal to the laser beam). The prior art bushings typically support the stent tubing, however, because the inner diameter of the support bushing is closely matched to the outer diameter of the stent tubing, there is some amount of drag or friction between the bushing and the stent tubing. The control system must supply sufficient force to overcome the inertia of the tubing and the drag caused by the interface between the bushing and the stent tubing, and at the same time accurately position the stent tubing for laser cutting. It is therefore a goal to reduce cutting errors due to sticking and choppiness in the movement of the stent tubing and to improve yields.
Accordingly, the manufacturers of stents have long recognized the need for improved manufacturing processes and to reduce the amount of friction between the bearing and the stent tubing during the laser cutting process. The present invention fulfills these needs.